Prevention and Detection of Overheating from Component Short Circuits

ABSTRACT

A personal electronic device can include a main printed circuit board having disposed thereon a processing unit, one or more auxiliary circuits coupled to the main printed circuit board by one or more corresponding flexible printed circuits and one or more temperature sensors disposed on one of the flexible printed circuits. A processing unit of the portable electronic device can be configured to monitor the one or more temperature sensors, provide a warning in response to a monitored temperature exceeding a first threshold, and to cause a shutdown of at least a portion of the personal electronic device in response to the monitored temperature exceeding a second threshold. The temperature sensors can be negative temperature coefficient resistors.

BACKGROUND

The recent proliferation of personal electronic devices has resulted ina significant increase in the number of electronic devices with which auser shares close physical proximity and often physical contact. Forexample, fitness monitors, smart watches, and other wearable devices maybe in physical contact with a user for all or a significant portion ofthe day. As a result, operating conditions and/or malfunctions of thevarious components within a personal electronic device may result inconditions that physiologically affect the user. One example can arisefrom an electrical fault (e.g., a short circuit) within a component ofthe personal electronic device. Such electrical faults can arise frommanufacturing defects, component aging, or other damage. The electricalfault can cause excessive current flow through the component, leading tounwanted power dissipation and an associated temperature increase thatmay cause discomfort to a user.

In such cases, it may be desirable to shut down the portable electronicdevice to prevent further damage to the device and/or discomfort to theuser. It may also be desirable for the electronic device to log theshutdown event and other data associated therewith and/or for the deviceto communicate to the user that the device should be returned forservicing. However, the extreme space constraints associated withpersonal electronic devices, and particularly with wearable personalelectronic devices, may complicate the addition of further faultdetection and mitigation circuitry. Thus, what is needed in the art areimproved techniques for detecting and isolating faults within a personalelectronic device.

SUMMARY

A personal electronic device can include a main printed circuit boardhaving thereon a processing unit, one or more auxiliary circuits coupledto the main printed circuit board by one or more corresponding flexibleprinted circuits and one or more temperature sensors disposed on one ofthe flexible printed circuits. A processing unit of the portableelectronic device can be configured to monitor the one or moretemperature sensors, provide a warning in response to a monitoredtemperature exceeding a first threshold, and to cause a shutdown of atleast a portion of the personal electronic device in response to themonitored temperature exceeding a second threshold. The temperaturesensors can be negative temperature coefficient resistors. Theprocessing unit can be a system on a chip.

The personal electronic device can further include a battery and a powerregulator. The processing unit disposed on the main printed circuitboard can be a power management unit configured to control the powerregulator to power the personal electronic device from the battery. Themain printed circuit board can have disposed thereon a system on a chipin addition to the power management unit.

The personal electronic device can be a wearable device, such as asmartwatch.

The personal electronic device may be further configured to provide awarning in response to a monitored temperature exceeding the firstthreshold by at least one of: logging an overtemperature warning in amemory of the personal electronic device and providing visual or audiblefeedback to a user of the portable electronic device, the visual oraudible feedback indicating an overtemperature warning. The personalelectronic device may be further configured to cause a shutdown of atleast a portion of the personal electronic device in response to themonitored temperature exceeding a second threshold by at least one of:logging a shutdown event in a memory of the personal electronic device,shutting down at least a portion of the personal electronic device, andproviding visual or audible feedback to a user of the portableelectronic device, the visual or audible feedback indicating anovertemperature shutdown. The personal electronic device can be furtherconfigured cause the personal electronic device to restart in a debugmode.

In other embodiments, a personal electronic device can include abattery, a regulator coupled to the battery and configured to power aplurality of loads, and a power management unit configured to operatethe regulator to power the plurality of loads. The power management unitcan be configured to monitor at least one of a current or power suppliedby the battery to the regulator or at least one of a current or powersupplied by the battery to the plurality of loads and to compare themonitored current or power to an expected current or power drawcorresponding to an operating state of the personal electronic device todetect an electrical fault with a component of the personal electronicdevice. The power management unit may be integrated with the regulator.Two or more of the plurality of loads are powered by a common bus fromthe regulator. The power management unit may be configured to detect anelectrical fault with a component of the personal electronic device byproviding a warning in response to the monitored current or powerexceeding the expected current or power draw corresponding to theoperating state of the personal electronic device by a first threshold,and causing a shutdown of at least a portion of the personal electronicdevice in response to the monitored current or power exceeding theexpected current or power draw corresponding to the operating state ofthe personal electronic device by a second threshold.

The processing unit may be further configured to provide a warning inresponse to the monitored current or power exceeding the expectedcurrent or power draw corresponding to the operating state of thepersonal electronic device by a first threshold by logging anovertemperature warning in a memory of the personal electronic device,and providing visual or audible feedback to a user of the portableelectronic device, the visual or audible feedback indicating anovertemperature warning. The processing unit may be further configuredto cause a shutdown of at least a portion of the personal electronicdevice in response to the monitored current or power exceeding theexpected current or power draw corresponding to the operating state ofthe personal electronic device by a second threshold by logging ashutdown event in a memory of the personal electronic device, shuttingdown at least a portion of the personal electronic device, providingvisual or audible feedback to a user of the portable electronic device,the visual or audible feedback indicating an overtemperature shutdown;and causing the personal electronic device to restart in a debug mode.The visual or audible feedback indicating an overtemperature shutdownmay indicate that a user should return the personal electronic devicefor service.

In still other embodiments, a method of detecting and mitigating anelectrical fault in a component of a personal electronic device caninclude monitoring a temperature of at least one temperature sensordisposed on a flexible printed circuit connecting a main printed circuitboard of the personal electronic device to an auxiliary circuit of thepersonal electronic device, providing a warning in response to themonitored temperature exceeding a first threshold, wherein providing awarning further includes logging an overtemperature warning in a memoryof the personal electronic device and providing visual or audiblefeedback to a user of the portable electronic device, the visual oraudible feedback indicating an overtemperature warning. Detecting andmitigating an electrical fault in a component of the personal electronicdevice can further include causing a shutdown of at least a portion ofthe personal electronic device in response to the monitored temperatureexceeding a second threshold, wherein causing a shutdown furtherincludes logging a shutdown event in a memory of the personal electronicdevice, shutting down at least a portion of the personal electronicdevice, and providing visual or audible feedback to a user of theportable electronic device, the visual or audible feedback indicating anovertemperature shutdown. Causing a shutdown can further include causingthe personal electronic device to restart in a debug mode. The one ormore temperature sensors can be negative temperature coefficientresistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a personal electronic device.

FIG. 2 illustrates a fault detection circuit for a personal electronicdevice.

FIGS. 3A and 3B illustrate a power distribution network of a personalelectronic device.

FIG. 4 illustrates a state diagram of a fault detection system for apersonal electronic device.

FIGS. 5A, 5B, 5C, 5D, and 5E illustrate a series of fault detectioncircuits.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousspecific details are set forth to provide a thorough understanding ofthe disclosed concepts. As part of this description, some of thisdisclosure's drawings represent structures and devices in block diagramform for sake of simplicity. In the interest of clarity, not allfeatures of an actual implementation are described in this disclosure.Moreover, the language used in this disclosure has been selected forreadability and instructional purposes, has not been selected todelineate or circumscribe the disclosed subject matter. Rather theappended claims are intended for such purpose.

Various embodiments of the disclosed concepts are illustrated by way ofexample and not by way of limitation in the accompanying drawings inwhich like references indicate similar elements. For simplicity andclarity of illustration, where appropriate, reference numerals have beenrepeated among the different figures to indicate corresponding oranalogous elements. In addition, numerous specific details are set forthin order to provide a thorough understanding of the implementationsdescribed herein. In other instances, methods, procedures and componentshave not been described in detail so as not to obscure the relatedrelevant function being described. References to “an,” “one,” or“another” embodiment in this disclosure are not necessarily to the sameor different embodiment, and they mean at least one. A given figure maybe used to illustrate the features of more than one embodiment, or morethan one species of the disclosure, and not all elements in the figuremay be required for a given embodiment or species. A reference number,when provided in a given drawing, refers to the same element throughoutthe several drawings, though it may not be repeated in every drawing.The drawings are not to scale unless otherwise indicated, and theproportions of certain parts may be exaggerated to better illustratedetails and features of the present disclosure.

FIG. 1 illustrates various components of a personal electronic device100. Personal electronic device 100 may include a main printed circuitboard 110, which may be connected to a plurality of auxiliary circuitboards or components 120, 130, 140, 140 a, and 150 via a plurality ofcorresponding flexible printed circuits 112, 113, 114, 114 a, and 115.Main printed circuit board 110 may have disposed thereon a variety ofcomponents, including a system on a chip (SoC) 110 a. SoC A10a mayinclude a processor (or processors), memory, input/output controllersand interfaces, and communication interfaces. The processor (orprocessors) may include a CPU for executing general purposeinstructions, a GPU for executing graphics-related instructions (orgeneral purpose computing instructions), and one or more otherspecialized processors for particular processing tasks. Any or all ofthe processors may be single core or multi-core processors. The memorymay include random access memory (RAM) for storing the data being actedupon by the processors and may also include storage memory in the formof flash memory or other non-volatile or read only memory. Theinput/output controllers and interfaces may include controllers andinterfaces for a display, one or more buttons, a touch screen, audiospeakers, and/or other I/O devices. The communication interfaces mayinclude various wired or wireless interfaces, such as universal serialbus (USB), wireless networking (WiFi, Bluetooth, etc.), and the like.The communication interfaces may include further interfaces such ascellular data, etc.

Also located on main printed circuit board 110 may be a power regulator110 b (discussed in greater detail below) and a transducer 110 c. Powerregulator 110 b may be used to convert electrical energy from a batteryin the personal electronic device to an appropriate voltage and currentfor the various components of the personal electronic device. In someembodiments, power regulator 110 b may also operate to receive a powerinput via a wired or wireless connection and convert the power input toa level suitable for charging the battery. Power regulator 110 b mayinclude a power management unit (PMU) for controlling the powerregulator, or a separate PMU may be provided. Transducer 110 c may beused to provide mechanical communication, such as vibrations or othertactile or haptic feedback to the user in response to variousconditions, such as arrival of a message, reminders about anappointment, etc. In one embodiment, personal electronic device 100 maybe a smartwatch/fitness monitor device, such as the Apple Watch, offeredfor sale by Apple Inc. of Cupertino, Calif.

In the case of a watch implementation, the main printed circuit board110, auxiliary circuit boards or components 120, 130, 140, 140 a, and150, and flex circuits 112, 113, 114, 114 a, and 115 may be folded tofit within a watch case (not shown). As a non-limiting example,auxiliary circuit board 120 may include the display and touchscreencomponents and flex circuit 112 may be folded over so that auxiliarycircuit board 120 is located above main circuit board 110 and forms oris in proximity to a face of the watch case. Similarly, auxiliaryprinted circuit board 140 may include components related to a heartratemonitor or other sensors that require physical contact with a user.Thus, flex circuit 114 may be folded under so that auxiliary circuitboard 140 is located below main circuit board 110 and is in contact orproximity with the back of the watch case, and thus the user. Auxiliarycircuitry 130 may include circuitry associated with controls on one sideof the watch, such as a rotating crown and/or one or more pushbuttons.Similarly, auxiliary circuitry 150 may include circuitry associated withother input or output devices such as a loudspeaker, microphone, etc.Flex circuits 113 and 115 may be bent as necessary so that auxiliarycircuits 130 and 150 may be disposed as necessary to accommodate thephysical design of the watch. In some embodiments, there may be flexconnectors that branch off of other flex connectors. For example, abattery 140 a may be connected via flex circuit 114 a to flex circuit114, which connects to main printed circuit 110, and specifically topower regulator 110 b. It will be appreciated by those skilled in theart that the foregoing describes one non-limiting example of how apersonal electronic device may be arranged, and that other arrangementsare also possible and may be desirable for particular implementations.

In some cases, a component of the personal electronic device may developan electrical fault (an internal short circuit, for example), thatcauses an excessive current draw. This excessive current draw can causea single component to draw an amount of power approaching or evengreater than the normal power draw of the entire personal electronicdevice. This excessive current draw can cause a temperature increasethat may physiologically impact the user. The level of current that cancause a user-physiology-affecting temperature increase may be differentfor different components, based on the proximity of that component tothe user. For example, in a watch application, a significant temperaturerise in a component on the watch back may be more likely to affect theuser than the same temperature rise in a component on the watch face.(Although it will be appreciated that the user may interact with allsides of the personal electronic device at varying times.) Additionally,a device drawing an abnormal current that is located near a thermallyconductive element (e.g., a metallic watch case) may have greater effecton the temperature increase felt by the user than one that is surroundedby thermally non-conductive materials. Thus, it may be desirable tomonitor the temperatures of various elements of the personal electronicdevice and shutdown those components and/or the device when anabnormally high temperature (as might be caused by an electrical faultis detected.

Temperature Sensors in Flex Circuits

In some cases, electronic components may have their own internaltemperature monitoring components. For example, SoC 110 a may includetemperature sensors deployed within it to monitor the temperature ofprocessor cores, radio transmitters, and the like. However, for manyauxiliary components, such internal temperature sensors may not beavailable. Additionally, due to space availability or other physicalconstraints, it may not be feasible to install temperature sensordevices on the various auxiliary printed circuit boards or components,120, 130, 140, 140 a, and 150. However, in such cases, thermal effectsof an increased current draw by a component may be detected by disposingtemperature sensors in the flexible printed circuit connectors thatcouple the auxiliary device to the main printed circuit board. In theexample illustrated in FIG. 1, temperature sensor 162 may be disposed inflex circuit 112, Two temperature sensors 163 a and 163 b may bedisposed in flex circuit 113. Temperature sensors 164, 164 a, and 165may be disposed in flex circuits 114, 114 a, and 115, respectively. Eachof these temperature sensors may be used to detect an increase intemperature of a corresponding auxiliary circuit board or component. Asdescribed in greater detail below, upon detection of such an increase,action may be taken to reduce or eliminate the physiological effect ofsuch temperatures on the user.

Temperature sensors 162, 163 a, 163 b, 164, 164 a, and 164 may take avariety of forms. The most commonly used electronic temperature sensorsare negative temperature coefficient (NTC) thermistors/resistors,resistance temperature detectors (RTDs), thermocouples, and varioussemiconductor based sensors. Semiconductor based sensors may beintegrated within various components. Thermocouples may be advantageousin that they are operable over wider temperature ranges than othersolutions. RTDs can provide highly accurate temperature readings. NTCresistors may exhibit relatively large, predictable, and precise changesin resistance that correlate with variation in temperature.Additionally, as temperature increase, the resistance of an NTC resistordecreases rapidly. As a result, relatively small temperature changes canbe detected quickly and accurately. Additionally, NTC resistors can besufficiently compact that incorporation into flex circuits isfacilitated.

Thus, in some embodiments, temperature sensors 162, 163 a, 163 b, 164,164 a, and 166 may be implemented, for example, as negative temperaturecoefficient (NTC) resistors disposed respectively in flex circuits 112,113, 114, 114 a, and 115. One temperature sensor may be provided foreach circuit, component, or group of circuits or components for whichtemperature monitoring is desired, which may include those circuits forwhich an electrical fault would cause a temperature increase that wouldphysiologically impact a user. The temperature sensors may be placed onthe flex circuit at any suitable location, taking into account proximityto the monitored component, proximity to other components that mightinterfere with the measurement, bending of the flex circuit, and otherfactors. As shown in FIG. 1, temperature sensor 162 is disposed in flexcircuit 112 near auxiliary circuit/board 120. Temperature sensor 165 isdisposed in the middle of flex circuit 115. Flex circuit 113 includestwo temperature sensors 163 a (located proximate auxiliary circuit/board130) and 163 b (located proximate main board 110). It will beappreciated that although it is possible to incorporate multipletemperature sensors in each flex circuit, it may be desirable in someimplementations to have only a single temperature monitor in each flex.In some embodiments, it may be desirable to not have a temperaturesensor in a given flex circuit if that flex circuit does not supply asystem or component for which temperature monitoring is desired.

FIG. 2 illustrates a circuit for monitoring the temperatures of thetemperature sensors 162, 163 a, 164, 164 a, and 164. This temperaturemonitoring circuit may be located in the power management unit (PMU).PMU-based temperature monitoring can have several advantages. First,some embodiments may already have certain temperature sensors in placeand being monitored by the PMU, and thus there may be certain structuresand systems in place to facilitate temperature monitoring. Additionally,by incorporating the temperature monitoring and related alarm andshutdown functions into the PMU, protection may be more power efficient,more highly available, more reliable, and/or faster than if serviced byanother system. For example, by incorporating temperature sensing in thePMU, protection will be available even when the SoC is off (such as aprocessor in the SoC, which may have other workloads and/or beunavailable at certain times).

With continued reference to the PMU circuitry illustrated in FIG. 2,each temperature sensor 162, 163 a, 164, 164 a, and 164 may be coupledto a corresponding switch SW1, SW2, SW3, SW4, and SW5, respectively. Theswitches SW1-SW5 may be operated by timer/control logic 270.Timer/control logic 270 may close switches SW1-SW5 one at a time insequence. Closing a switch allows current from current source 272(coupled to voltage rail 274) to flow through one of the temperaturesensors. This produces a voltage that is coupled to the (inverting)input of warning comparator 282 and to the (inverting) input of shutdowncomparator 284. A series of reference voltages VREF1 and VREF2 may beselectively coupled to the (non-inverting) input of warning comparator282. Similarly, a series of reference voltages VREF3 and VREF4 may beselectively coupled to the (non-inverting) input of shutdown comparator284. The reference voltages to which the various temperature sensorvoltages are compared form the thresholds for generating anovertemperature warning (comparator 282) or an overtemperature shutdown(comparator 284).

Multiple reference voltages may be provided so that different voltagethresholds (and therefore temperature thresholds) may be used for thetemperature warning and temperature shutdown triggers for differentcomponents corresponding to the different temperature sensors. Switches281 may be operated to couple any one of the overtemperature warningreference voltages VREF1 or VREF2 to warning comparator 282. Similarly,switches 283 may be operated to couple any one of the overtemperatureshutdown reference voltages VREF3 or VREF4 to shutdown comparator 284.Although two reference voltages are illustrated for both the warning andshutdown comparators, a single reference voltage may be used for alltemperature sensors, a different reference voltage may be used for eachtemperature sensors, or some temperature sensors may have a uniquereference voltage, while others have a shared reference voltage. Theswitches 281 and 283 coupling the reference voltages to their respectivecomparators may also all be selectively opened to decouple the referencevoltages from the comparators reducing the quiescent power consumptionof the circuit when thermal measurements are not being made. Inalternative embodiments, switches SW1-SW5 may be opened to reducequiescent current when measurements are not being made. In someembodiments, to further reduce quiescent power consumption, an enablesignal may be provided to warning comparator 282 and shutdown comparator284 to prevent the comparators from operating when temperaturemeasurements are not being made. Furthermore, shutdown comparator 284may be further disabled until it receives an enable signal from theoutput of warning comparator 282, meaning that shutdown comparator 284does not operate until warning comparator 282 has been triggered by awarning-level over temperature condition.

As an alternative to the circuitry illustrated in FIG. 2, othertemperature comparison circuit structures could be implemented in thePMU. In one embodiment digital to analog converters (DACs) withprogrammable settings for each temperature sensor could be used to applydifferent references to the non-inverting terminal of the comparator. Inother embodiments, instead of comparators, a finite state machinedriving a switch matrix to the input of an analog to digital converter(ADC) could be used, allowing the overtemperature comparisons to beperformed in the digital domain.

A variety of temperature sensing circuits are illustrated in FIGS.5A-5E. FIG. 5A includes a constant current source 501 that drivescurrent through a temperature sensor, such as NTC resistor 502. Analogto digital converter 503 is configured to sample the analog voltage 504generated across temperature sensor 502 relative to ground and convertthis sampled value to a digital reading 505. This digital reading maythen be compared by a processing element 506 to one or more voltagethresholds V1 and V2, such as an overtemperature warning threshold andan overtemperature shutdown threshold as discussed above. The processingelement 506 may be control logic implemented the power management unit,either as discrete logic circuitry, a field programmable gate array, aprogrammed processor, or other suitable circuit structure. In otherembodiments, processing element 506 may be part of a processing elementof the electronic device, such as a CPU or other processing component.

FIG. 5B illustrates an alternative sensing circuit structure in which adigital current source 511 may generate one or more programmed currentvalues I1, I2. These digitally programmed current values 512 are inputinto digital to analog converter 513. Digital to analog converter 513generates an output current I that is driven through a temperaturesensor, such as NTC resistor 514. As in the embodiments described above,this generates a voltage V, that may be measured by comparator circuitry(not shown) similar to that described above with respect to FIG. 2. Inthis embodiment, the digitally programmed current source may beconfigured to provide different currents to different temperaturesensors (not shown) to provide for improved sensing in arrangementswhere different levels of sensitivity are desirable.

FIG. 5C illustrates yet another alternative sensing circuit structure.In FIG. 5C, a current source 521 drives a constant current throughtemperature sensor 522, which may be an NTC resistor. This generates avoltage 523 that is a function of temperature. The voltage 523 is inputinto a hysteretic comparator 524. Hysteretic comparator 524 compares thesensed voltage 523 to reference voltage V1. The output of hystereticcomparator 524 is delivered to analog to digital converter 525, whichconverts the analog output of the hysteretic comparator to a digitalvalue that is provided to processing element 526. As above, processingelement 526 may preferably be part of the PMU, or, in other embodiments,may be part of another component of the electronic device. Processingelement may monitor the hysteretic comparator output to detect anovertemperature warning or shutdown condition as described above.

FIG. 5D illustrates still another alternative temperature sensingcircuit structure. In FIG. 5D, the temperature sensor, e.g., NTCresistor 533 is incorporated into an oscillator circuit. Morespecifically, a voltage rail 531 is divided by the series combination ofa capacitor 532 and temperature sensor 533. Capacitor 532 may start in adischarged, i.e., zero voltage state. As capacitor 532 charges, voltage504 provided to the inverting input of an operational amplifier 535,will decrease, ultimately reaching zero when capacitor 532 is fullycharged to the rail voltage 531. This action will produce acorresponding inverted voltage (i.e., increasing voltage) at the outputof operational amplifier 533. When the output of operational amplifier535 reaches a predetermined threshold, switching device 534 may beactivated, which discharges capacitor 532 and pulls voltage 504 up tothe voltage of rail 531. This also forces the output of operationalamplifier 535 low. Switch 534 then opens, and the cycle repeats. Theresistance value of temperature sensor 533, which varies withtemperature, can determine the rate at which capacitor 532 charges,which determines the frequency of the oscillations appearing at theoutput of operational amplifier 535. Frequency detector 536 may beprovided to determine the frequency of the output of operationalamplifier 535, which is a function of the temperature detected. Thistemperature measurement may then be compared against warning andshutdown thresholds as described above.

FIG. 5E illustrates one further temperature sensing circuit structure.In the temperature sensing circuit of FIG. 5E, temperature sensor 541(e.g., an NTC resistor) is incorporated into the feedback loop ofoperational amplifier 542. The feedback loop also includes fixedresistance 543. As the resistance value of temperature sensor 541changes with temperature, the gain of operational amplifier 542 willchange proportionally. With a fixed voltage Vref provided to the otherinput of the operational amplifier, the voltage appearing at the outputwill be Vref times the gain of operational amplifier. The output voltagefrom operational amplifier 542 may be provided to a comparator or analogto digital converter 544 in accordance with one of the embodimentsdescribed above.

The PMU circuitry illustrated in FIGS. 2 and 5 and described above maybe operated as follows to provide temperature protection for a portableelectronic device. A measure temperature signal may be received byprogrammable timer and control logic 270. The measure temperaturessignal may also be provided as an enable signal to overtemperaturewarning comparator 282 and overtempt shutdown comparator 284 asdescribed above. When programmable controller 270 receives the measuretemperature signal it may provide drive signals to sequentially closeand open each of switches SW1, SW2, SW3, SW4, and SW5 to allow currentsource 272 to individually flow through the temperature sensors 162,163, 164, 164 a, and 165, respectively. The flow of fixed current fromcurrent source 272 will produce a voltage that is a function oftemperature sensed by the respective temperature sensors. This voltagemay fed to overtemperature warning comparator 282 and overtemperatureshutdown comparator 284 and compared to the selected thresholds asdiscussed above. If the sensed voltage exceeds an overtemperaturewarning threshold, the output of overtemperature warning comparator 282may provide an overtemperature warning signal to any suitable componentwithin the personal electronic device. If the sensed voltage exceeds anovertemperature shutdown threshold, the output of the overtemperatureshutdown comparator 284 may provide an overtemperature shutdown signalto the PMU, causing a shutdown of the personal electronic device.

In other embodiments, instead of or in addition to comparing themeasured temperature to selected thresholds to determine anovertemperature warning or overtemperature shutdown condition, the rateof change of temperature over consecutive measurement cycles may be usedto further characterize a fault condition. For example, a higher rate oftemperature rise may be more indicative of a fault. Additionally, byrelying on rate of rise instead of or in addition to a simple thresholdcomparison, it may be possible to prevent false alarms associated with auser entering a substantially warmer environment with the personalelectronic device. Implementation of a system relying on rate of changemay incorporate a sampling and analog to digital converter circuit forsampling and storing the various temperature measurements in a memoryaccessible by the SoC or PMU, and additional programming or otherconfiguration within the SoC or PMU to analyze samples to determine arate of change, with a suitable rate of change threshold being used totrigger an overtemperature warning or overtemperature shutdowncondition.

Programmable timer and control logic 270 may provide suitable timing forthe temperature signals. For example, it may be desirable to providecontinuous scanning of the various temperature sensors. In such anapplication, the programmable timer and control logic may cycle througheach temperature sensor in a round robin fashion, such that each sensoris read for a portion of the total round robin cycle time. In general,the round robin time will be determined by balancing how quickly thesystem should detect and respond to an overtemperature condition againstthe increased power requirements of longer and/or more frequentmonitoring times. In one embodiment, a round robin time of 20milliseconds, with a 100 microsecond sample time for each temperaturesensor may be used, although these values are merely exemplary, andother suitable values could also be used. A suitable debounce time mayalso be provided. In one embodiment, a suitable debounce time may be 200microseconds, although other suitable values could also be used. Becausethe SoC or PMU will know the timing profile associated with thetemperature sensing operation, it will be able to ascertain which systemtriggered an overcurrent warning or overcurrent shutdown by the time atwhich it occurs.

When the PMU receives an overtemperature warning from overtemperaturewarning comparator 282, it may take various actions. For example, it maylog the overtemperature warning in a memory with the time, temperaturerecorded (by an analog to digital converter, not shown), component orsystem responsible for the overtemperature warning, and otherinformation about the operating conditions of the personal electronicdevice at the time the warning was recorded. (This logging function mayalso or alternatively be performed by the Soc.) This information may beused at a later time for diagnostics or troubleshooting if the problempersists. When an overtemperature shutdown signal from shutdowncomparator 284, is generated, the PMU (and optionally/additionally theSoC) may take further actions. For example, it may log theovertemperature information as described above with respect to theovertemperature warning. More importantly, the PMU may shut down eitherthe component causing the overtemperature condition or the entirepersonal electronic device. In some embodiments (such as thoseillustrated in FIG. 3A, discussed below), it may be possible anddesirable to shut down an individual system/subsystem, leaving the restof personal electronic device operational. In other embodiments, becauseof the interdependent nature of the various subsystems of the portableelectronic device, operation of the personal electronic device with oneor more subsystems shut down may sufficiently compromise overalloperation of the device that a full shutdown is preferable.Additionally, in some embodiments, the nature of the power distributionnetwork of the device may not allow for individual subsystems to be shutdown.

In any case, when the PMU shuts down all or part of the personalelectronic device because of an overtemperature shutdown condition, itmay also cause feedback to be provided to the user indicating that thepersonal electronic device (or a portion thereof) has been shut down andthat the user should return the device for service. This feedback may beprovided in the form of visual information on a display of the portableelectronic device and/or with audio warnings such as beeps, etc.Additionally, the PMU may be configured to make the shutdown either aone-time event, in which case the personal electronic device (orsubsystem) may be restarted after a suitable time delay, or a permanentshutdown, in which case the device (or subsystem) is prevented fromrestarting without intervention by authorized service personnel. In thislatter case, it may be particularly desirable to provide some sort offeedback to the user indicating that the personal electronic deviceshould be taken to in for service.

Monitor Battery Current Profile

The foregoing arrangements for detection and mitigation of circuitfaults that may result in an overtemperature condition physiologicallyimpacting a user of a personal electronic device rely on placement oftemperature sensors, such as negative temperature coefficient resistors,in the flex circuits of the personal electronic device. However, in someembodiments, such circuit faults may be detected in other ways. Morespecifically, it may be possible and/or desirable to detect a circuitfault by monitoring a current profile, such as a discharge profile of abattery of the personal electronic device, to detect a current draw thatis inconsistent with the expected current draw for a given operatingcondition. Monitoring the discharge profile of the battery can includemonitoring the battery current, instantaneous power, or average powerover a longer time period. This monitoring may be performed by a PMU(power management unit), PMIC (power management integrated circuit), orBMU (battery management unit) or by some combination of these devices oranother processing system or dedicated circuitry within the portableelectronic device.

FIGS. 3A and 3B illustrate block diagrams of exemplary powerdistribution systems 300 a and 300 b for personal electronic devices.Power distribution systems 300 a and 300 b each include a battery 301that provides power for the various loads (304, 305, 306). Power isprovided via regulator 302, which may take a variety of forms. Regulator302 may, for example, be a switching regulator, such as a buckconverter, boost converter, buck-boost converter, etc. In someembodiments, regulator 302 may be a bidirectional regulator that canalso receive power from an external power source 307 to charge battery301. Regulator 302 may include an integrated power management unit, ormay be controlled by a separate power management unit 303. The powerdistribution systems 300 a and 300 b differ in the number of busses usedto supply power from regulator 302 to loads 304, 305, and 306. Powerdistribution system 300 a provides a separate bus to each load. In thiscase, the voltage to each load may be separately regulated, andindividual loads may be monitored and/or isolated as desired. Powerdistribution system 300 b provides a combined bus that subdivides topower each load. In the latter case voltage to each load is commonlyregulated, and it may be more difficult or impossible to monitor and/orisolate individual loads.

In either case, PMU 303 may be configured to monitor the load current ofthe regulator. (As noted above, this monitoring could also be performedby another component, such as a battery management unit.) In powerdistribution system 300 a, the load current to each load may beseparately monitored. This individual load current may be compared to athreshold to determine whether a particular load is drawing a highercurrent than it should for a given operating condition. For example, adisplay may draw a higher current when it is activated and a lowercurrent when it is deactivated. Other components may draw a morecontinuous load current. In either case, the PMU (or the BMU or SoC) maycompare the present current to a threshold associated with thecorresponding operating condition to determine whether an overcurrentcondition exists. As above, with the direct temperature sensingembodiments, there may be multiple thresholds, for example a relativelylower threshold associated with an overcurrent warning level and arelatively higher threshold associated with an overcurrent shutdownlevel. When current exceeding a selected threshold is exceeded, thecorresponding warning or shutdown condition may be activated, either forthe offending load, or for the system as a whole, as discussed abovewith respect to the direct temperature sensing embodiments.

In power distribution system 300 b, it may not be practical or evenpossible to monitor individual load currents because of the common bus.In this case, an aggregate current for the device may be monitored. Thisaggregate current may be the output current of the regulator 302supplied to the loads, or may even be the input current from the battery301 to the regulator 302. This monitored aggregate current can becompared to the expected aggregate current for the state of the deviceto determine whether any component is drawing substantially more currentthan it should, which could be indicative of an electrical fault. Table1, below, illustrates exemplary power profiles (which may be equated tocurrent draws) to detect an electrical fault when an expected power drawis exceeded. The values given are merely exemplary, and may vary widelydepending on a particular implementation.

Idle Low High Component Power State Power State Power State Load 1:Touch Display 0.05 W 0.25 W  0.5 W Load 2: CPU  0.1 W 0.5 W 1.0 W Load3: Communications 0.05 W 0.4 W 0.75 W 

As can be seen from Table 1 and FIGS. 3A and 3B, a personal electronicdevice may include Load 1 304, a touch sensing display, Load 2 305, aCPU (or, more generally, an SoC), and Load 3 306, a communicationssystem incorporating WiFi, Bluetooth, cellular, and/or other types ofnetworking/communication equipment. Each of these systems may have anidle power state, a low power state, and a high power states. (There mayalso be other components and/or fewer or additional power states for thevarious components.) In the illustrated example, touch display 304 mayconsume 0.05 W when idle, i.e., when not displaying information butavailable to accept touch input. Touch display 304 may also consume 0.25W when in a low power state, corresponding, for example to a low screenbrightness setting and 0.5 W when in a high power state, corresponding,for example to a high screen brightness setting. CPU or, more generally,SoC 305 may consume 0.1 W in an idle state, 0.5 W in a low power state(corresponding to a light processing load), and 1 W in a high powerstate (corresponding to a high processing load). Communication module306 may consume 0.05 W in an idle state, 0.4 W in a low power state(corresponding to receiving data) and 0.75 W in a high power states(corresponding to transmitting data).

By knowing the current operating state, the SoC and/or PMU can determinewhat is an appropriate level of power draw for the personal electronicdevice. In embodiments in which power delivered to individual subsystemsmay be monitored (e.g., FIG. 3A), if any subsystem is drawing more thanexpected for its current state, a fault may be detected/indicated.Alternatively, in embodiments in which only aggregate current or powersupplied may be monitored (e.g., FIG. 3B), if the total system load isgreater than anticipated based on the sum of the individual powerconsumptions for the various subsystems in their present states, a faultmay be detected/indicated. It will be appreciated that such anarrangement may not detect/indicated a fault if the current or energyconsumption due to a fault is less than the expected current or powerconsumption for that operating state. For example, if all components arein the idle state, the expected power draw is 0.2 W. If, instead,battery 301 and/or Regulator 302 are delivering 1 W when all componentsare in the idle state, it may be determined that a component hasfaulted. Thus, a warning may be logged and/or provided to the user, ashutdown may be performed, or, in some embodiments, it may be desired toperform a restart of the device to determine whether the excessive powerdraw is caused by a component being hung in a wrong operating mode. Iffurther warnings are logged, then a shutdown may be performed.Additionally, the shutdown may include a lockout as described above anda message may be displayed to the user to return the personal electronicdevice for service.

It should be noted that the prior example is capable of detecting afault current corresponding to a power draw of 0.8 W, even though thepower draw is less than the personal electronic device might experienceat other times. For example, if all systems are operating in the lowpower state, the expected power draw is 1.15 W, which is more than the0.8 W triggering the warning or shutdown discussed above. Similarly, ifall systems are operating in the high power state, the expected powerdraw is 2.25 W. It will be further appreciated that different operatingstates or combinations of operating states will result in differentexpected power draws. The SoC or PMU can be programmed to look for powerdraws exceeding the expected power draw by a predetermined thresholdamount for all expected combinations of power draw states.

In addition or as an alternative to monitoring instantaneous currentdraw or instantaneous power consumption for fault detection, the systemmay be configured to monitor these parameters over time for faultdetection. For example, total battery charge consumed over a given timeperiod (i.e., current times time) or total energy consumed over a giventime period (i.e., power times time) to detect a fault current. Manypersonal electronic devices will include some form of “gas gauge”circuit (such as a battery management unit or BMU) that monitors somecombination of battery current, temperature, and voltage to determinethe battery state of charge. By monitoring the change in state of chargeor change in energy consumption over time, the increased charge orenergy consumption associated with a faulted device may be detected. Asabove, such a system may be implemented by having charge consumed perunit time thresholds, such as a first threshold associated with awarning level and a second, higher threshold, associated with a shutdownlevel.

FIG. 4 illustrates a state diagram 400 of a fault detection andmitigation system for a personal electronic device as described above.State diagram 400 is applicable to either sensing arrangement, i.e., thetemperature sensor disposed in the flex connector arrangement describedwith respect to FIGS. 1 and 2 or the aggregate current sensingarrangement described with respect to FIGS. 3A and 3 b. The system maystart in an off state 402. In the off state, both the PMU and the SoCare powered off. When the device is awakened, if no fault flag haspreviously been set, the personal electronic device may transition tothe monitor state 404. In the monitor state, the PMU may operate asrequired to supply sufficient power to the personal electronic device(“PED”). The PMU may also monitor the temperature sensors (such as anNTC resistor disposed in the flex) or the aggregate current. The SoC maybe in whatever state is required to achieve desired operation of thepersonal electronic device. (As noted above, in some embodiments, thetemperature/current monitoring may be performed by the SoC directlyrather than by the PMU.)

If, while in monitor state 404, a current fault is detected (i.e.,FAULT=1), the system may transition to the fault detected state 406. Inthe fault detected state, the PMU (or SoC, depending on which device isdoing the monitoring), may save data identifying the faulted system orsystems. While in the fault detected state 406 (and before transitioningto the host interrupted state 408), the SoC may continue to operate asrequired for the present operating condition of the personal electronicdevice. The PMU may also issue an interrupt signal (IRQ=1) to the SoC,allowing the SoC to respond to the fault as necessary. As describedabove, this may include a warning, a shutdown, a notification to theuser, etc. This interrupt signal (IRQ=1), may cause a transition to hostinterrupted state 408. In host interrupted state 408, the PMU may set afault flag (FAULT_FLAG=1) to prevent the device from restarting in tothe normal monitor state 404. The PMU may also shutdown if warranted (asdescribed above). Also in host interrupted state 408, the SoC can readthe faulted channel data from the PMU and store it in a non-volatilememory (i.e., store in memory an indication of which component orsubsystem is faulty).

If the system is in the off state 402 and starts when the fault flagdescribed above is set, the system may transition to the debug state410. In the debug state, the PMU may power up the non-faulted powerrails of the system (based on the faulty channel ID data stored inmemory by the SOC in the preceding host interrupted state 408).Additionally, the fault flag set by the PMU may be reset to allow fordebugging. Additionally, in the debug state 410, the SoC may beconfigured and/or programmed to allow for debugging mode that allowsdiagnostics to be performed and systems to be reset as necessarydepending on the repair accomplished, etc.

Described above are various features and embodiments relating to circuitfault detection and mitigation in personal electronic devices. Suchregulators may be used in a variety of applications, but may beparticular advantageous when used in conjunction with portableelectronic devices such as mobile telephones, smart phones, tabletcomputers, laptop computers, media players, and the like, as well as theperipherals associated therewith. Such associated peripherals caninclude input devices (such as keyboards, mice, touchpads, tablets, andthe like), output devices (such as headphones or speakers), storagedevices, or any other peripheral.

Additionally, although numerous specific features and variousembodiments have been described, it is to be understood that, unlessotherwise noted as being mutually exclusive, the various features andembodiments may be combined in any of the various permutations in aparticular implementation. Thus, the various embodiments described aboveare provided by way of illustration only and should not be constructedto limit the scope of the disclosure. Various modifications and changescan be made to the principles and embodiments herein without departingfrom the scope of the disclosure and without departing from the scope ofthe claims.

1. A personal electronic device comprising: a battery; a powerregulator; a main printed circuit board having disposed thereon a powermanagement unit configured to control the power regulator to power thepersonal electronic device from the battery; one or more auxiliarycircuits coupled to the main printed circuit board by one or moreflexible printed circuits corresponding to the one or more auxiliarycircuits; and one or more temperature sensors, wherein each temperaturesensor is disposed on one of the flexible printed circuits; wherein thepower management unit is configured to monitor the one or moretemperature sensors, provide a warning in response to a monitoredtemperature exceeding a first threshold, and to cause a shutdown of atleast a portion of the personal electronic device in response to themonitored temperature exceeding a second threshold.
 2. The personalelectronic device of claim 1 wherein the one or more temperature sensorsare negative temperature coefficient resistors.
 3. The personalelectronic device of claim 2 wherein the one or more negativetemperature coefficient resistors are driven by a current source.
 4. Thepersonal electronic device of claim 3 wherein the current source is adigitally programmable current source.
 5. The personal electronic deviceof claim 2 further comprising an analog to digital converter configuredto output a digital representation of a voltage across the one or morenegative temperature coefficient resistors.
 6. The personal electronicdevice of claim 2 comprising one or more temperature sensing circuitswherein the one or more negative temperature coefficient resistorsaffect a frequency of an oscillator as a function of temperature.
 7. Thepersonal electronic device of claim 2 comprising one or more temperaturesensing circuits wherein the one or more negative temperaturecoefficient resistors affect a gain of an amplifier as a function oftemperature.
 8. The personal electronic device of claim 1 wherein thepower management unit is integral with the power regulator.
 9. Thepersonal electronic device of claim 1 wherein the main printed circuitboard has disposed thereon a system on a chip in addition to the powermanagement unit.
 10. The personal electronic device of claim 1 whereinthe personal electronic device is a wearable device.
 11. The personalelectronic device of claim 5 wherein the personal electronic device is awatch.
 12. The personal electronic device of claim 1 wherein the powermanagement unit is configured to provide a warning in response to amonitored temperature exceeding the first threshold by at least one of:logging an overtemperature warning in a memory of the personalelectronic device; and providing visual or audible feedback to a user ofthe portable electronic device, the visual or audible feedbackindicating an overtemperature warning.
 13. The personal electronicdevice of claim 1 wherein the power management unit is configured tocause a shutdown of at least a portion of the personal electronic devicein response to the monitored temperature exceeding a second threshold byat least one of: logging a shutdown event in a memory of the personalelectronic device; shutting down at least a portion of the personalelectronic device; and providing visual or audible feedback to a user ofthe portable electronic device, the visual or audible feedbackindicating an overtemperature shutdown.
 14. The personal electronicdevice of claim 8 wherein the power management unit is furtherconfigured cause the personal electronic device to restart in a debugmode.
 15. A method of detecting and mitigating an electrical fault in acomponent of a personal electronic device, the method comprising:monitoring, by a power management unit of the personal electronicdevice, a temperature of at least one temperature sensor disposed on aflexible printed circuit connecting a main printed circuit board of thepersonal electronic device to an auxiliary circuit of the personalelectronic device; providing, by a power management unit of the personalelectronic device, a warning in response to the monitored temperatureexceeding a first threshold, providing a warning further comprising:logging an overtemperature warning in a memory of the personalelectronic device; and providing visual or audible feedback to a user ofthe portable electronic device, the visual or audible feedbackindicating an overtemperature warning; and causing, by a powermanagement unit of the personal electronic device, a shutdown of atleast a portion of the personal electronic device in response to themonitored temperature exceeding a second threshold, causing a shutdownfurther comprising: logging a shutdown event in a memory of the personalelectronic device; shutting down at least a portion of the personalelectronic device; and providing visual or audible feedback to a user ofthe portable electronic device, the visual or audible feedbackindicating an overtemperature shutdown.
 16. The method of claim 15wherein causing a shutdown further comprises cause the personalelectronic device to restart in a debug mode.
 17. The method of claim 15wherein the one or more temperature sensors are negative temperaturecoefficient resistors.
 18. A power management unit configured to monitorone or more temperature sensors disposed throughout a personalelectronic device, provide a warning in response to a monitoredtemperature exceeding a first threshold, and to cause a shutdown of atleast a portion of the portable electronic device in response to themonitored temperature exceeding a second threshold.
 19. The powermanagement unit of claim 18 wherein the one or more temperature sensorsare negative temperature coefficient resistors.
 20. The power managementunit of claim 19 wherein the one or more negative temperaturecoefficient resistors are driven by a current source.
 21. The powermanagement unit of claim 20 wherein the current source is a digitallyprogrammable current source.
 22. The power management unit of claim 19further comprising an analog to digital converter configured to output adigital representation of a voltage across the one or more negativetemperature coefficient resistors.
 23. The power management unit ofclaim 19 comprising one or more temperature sensing circuits wherein theone or more negative temperature coefficient resistors affect afrequency of an oscillator as a function of temperature.
 24. The powermanagement unit of claim 19 comprising one or more temperature sensingcircuits wherein the one or more negative temperature coefficientresistors affect a gain of an amplifier as a function of temperature.25. The power management unit of claim 18 wherein the power managementunit is integral with the power regulator.